Work function adjustment in a high-k gate electrode structure after transistor fabrication by using lanthanum

ABSTRACT

The work function of a high-k gate electrode structure may be adjusted in a late manufacturing stage on the basis of a lanthanum species in an N-channel transistor, thereby obtaining the desired high work function in combination with a typical conductive barrier material, such as titanium nitride. For this purpose, in some illustrative embodiments, the lanthanum species may be formed directly on the previously provided metal-containing electrode material, while an efficient barrier material may be provided in the P-channel transistor, thereby avoiding undue interaction of the lanthanum species in the P-channel transistor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the present disclosure relates to the sophisticatedintegrated circuits including transistor elements comprising highlycapacitive gate structures on the basis of a metal-containing electrodematerial and a high-k gate dielectric of increased permittivity comparedto conventional gate dielectrics, such as silicon dioxide and siliconnitride.

2. Description of the Related Art

The fabrication of advanced integrated circuits, such as CPUs, storagedevices, ASICs (application specific integrated circuits) and the like,requires the formation of a large number of circuit elements on a givenchip area according to a specified circuit layout, wherein field effecttransistors represent one important type of circuit element thatsubstantially determines performance of the integrated circuits.Generally, a plurality of process technologies are currently practiced,wherein, for many types of complex circuitry, including field effecttransistors, MOS technology is currently one of the most promisingapproaches due to the superior characteristics in view of operatingspeed and/or power consumption and/or cost efficiency. During thefabrication of complex integrated circuits using, for instance, MOStechnology, millions of transistors, e.g., N-channel transistors and/orP-channel transistors, are formed on a substrate including a crystallinesemiconductor layer. A field effect transistor, irrespective of whetheran N-channel transistor or a P-channel transistor is considered,typically comprises so-called PN junctions that are formed by aninterface of highly doped regions, referred to as drain and sourceregions, with a slightly doped or non-doped region, such as a channelregion, disposed adjacent to the highly doped regions. In a field effecttransistor, the conductivity of the channel region, i.e., the drivecurrent capability of the conductive channel, is controlled by a gateelectrode formed adjacent to the channel region and separated therefromby a thin insulating layer. The conductivity of the channel region, uponformation of a conductive channel due to the application of anappropriate control voltage to the gate electrode, depends on the dopantconcentration, the mobility of the charge carriers and, for a givenextension of the channel region in the transistor width direction, onthe distance between the source and drain regions, which is alsoreferred to as channel length. Hence, in combination with the capabilityof rapidly creating a conductive channel below the insulating layer uponapplication of the control voltage to the gate electrode, theconductivity of the channel region substantially affects the performanceof MOS transistors. Thus, as the speed of creating the channel, whichdepends on the conductivity of the gate electrode, and the channelresistivity substantially determine the transistor characteristics, thescaling of the channel length, and associated therewith the reduction ofchannel resistivity and increase of gate resistivity, is a dominantdesign criterion for accomplishing an increase in the operating speed ofthe integrated circuits.

Presently, the vast majority of integrated circuits are based on silicondue to substantially unlimited availability, the well-understoodcharacteristics of silicon and related materials and processes and theexperience gathered during the last 50 years. Therefore, silicon willlikely remain the material of choice for future circuit generationsdesigned for mass products. One reason for the dominant importance ofsilicon in fabricating semiconductor devices has been the superiorcharacteristics of a silicon/silicon dioxide interface that allowsreliable electrical insulation of different regions from each other. Thesilicon/silicon dioxide interface is stable at high temperatures and,thus, allows the performance of subsequent high temperature processes,as are required, for example, for anneal cycles to activate dopants andto cure crystal damage without sacrificing the electricalcharacteristics of the interface.

For the reasons pointed out above, in field effect transistors, silicondioxide is preferably used as a gate insulation layer that separates thegate electrode, frequently comprised of polysilicon or othermetal-containing materials, from the silicon channel region. In steadilyimproving device performance of field effect transistors, the length ofthe channel region has continuously been decreased to improve switchingspeed and drive current capability. Since the transistor performance iscontrolled by the voltage supplied to the gate electrode to invert thesurface of the channel region to a sufficiently high charge density forproviding the desired drive current for a given supply voltage, acertain degree of capacitive coupling, provided by the capacitor formedby the gate electrode, the channel region and the silicon dioxidedisposed therebetween, has to be maintained. It turns out thatdecreasing the channel length requires an increased capacitive couplingto avoid the so-called short channel behavior during transistoroperation. The short channel behavior may lead to an increased leakagecurrent and to a dependence of the threshold voltage on the channellength. Aggressively scaled transistor devices with a relatively lowsupply voltage and thus reduced threshold voltage may suffer from anexponential increase of the leakage current while also requiringenhanced capacitive coupling of the gate electrode to the channelregion. Thus, the thickness of the silicon dioxide layer has to becorrespondingly decreased to provide the required capacitance betweenthe gate and the channel region. For example, a channel length ofapproximately 0.08 μm may require a gate dielectric made of silicondioxide as thin as approximately 1.2 nm. Although, generally, high speedtransistor elements having an extremely short channel may preferably beused for high speed applications, whereas transistor elements with alonger channel may be used for less critical applications, such asstorage transistor elements, the leakage current caused by directtunneling of charge carriers through an ultra-thin silicon dioxide gateinsulation layer may reach values for an oxide thickness in the range of1-2 nm that may not be compatible with thermal design power requirementsfor performance driven circuits.

Therefore, replacing silicon dioxide as the material for gate insulationlayers has been considered, particularly for extremely thin silicondioxide gate layers. Possible alternative materials include materialsthat exhibit a significantly higher permittivity so that a physicallygreater thickness of a correspondingly formed gate insulation layerprovides a capacitive coupling that would be obtained by an extremelythin silicon dioxide layer. Therefore, it has thus been suggested toreplace silicon dioxide with high permittivity materials, such astantalum oxide (Ta₂O₅) with a k of approximately 25, strontium titaniumoxide (SrTiO₃) having a k of approximately 150, hafnium oxide (HfO₂),HfSiO, zirconium oxide (ZrO₂) and the like.

Additionally, transistor performance may be increased by providing anappropriate conductive material for the gate electrode to replace theusually used polysilicon material, since polysilicon may suffer fromcharge carrier depletion at the vicinity of the interface to the gatedielectric, thereby reducing the effective capacitance between thechannel region and the gate electrode. Thus, a gate stack has beensuggested in which a high-k dielectric material provides enhancedcapacitance based on the same thickness as a silicon dioxide layer,while additionally maintaining leakage currents at an acceptable level.On the other hand, the non-polysilicon material, such as titaniumnitride and the like, may be formed so as to connect to the high-kdielectric material, thereby substantially avoiding the presence of adepletion zone. Since, typically, a low threshold voltage of thetransistor, which represents the voltage at which a conductive channelforms in the channel region, is desired to obtain the high drivecurrents, commonly, the controllability of the respective channelrequires pronounced lateral dopant profiles and dopant gradients, atleast in the vicinity of the PN junctions. Therefore, so-called haloregions are usually formed by ion implantation in order to introduce adopant species whose conductivity type corresponds to the conductivitytype of the remaining channel and semiconductor region to “reinforce”the resulting PN junction dopant gradient after the formation ofrespective extension and deep drain and source regions. In this way, thethreshold voltage of the transistor significantly determines thecontrollability of the channel, wherein a significant variance of thethreshold voltage may be observed for reduced gate lengths. Hence, byproviding an appropriate halo implantation region, the controllabilityof the channel may be enhanced, thereby also reducing the variance ofthe threshold voltage, which is also referred to as threshold roll-off,and also reducing significant variations of transistor performance witha variation in gate length.

On the other hand, the threshold voltage depends, in addition to thespecific transistor configuration as described above, strongly on thework function of the gate electrode structure, which may beappropriately adjusted to the conductivity type and also to specifictransistor characteristics, such as gate length and the like. Theadaptation of the work function of the metal-containing electrodematerial may typically be accomplished by providing specific metal ormetal alloys to obtain the required work function. It turns out,however, that presently the number of promising material candidates foradjusting the work function of sophisticated transistor elements may bemoderately low, in particular when handling of these metals has toaccomplished in very sophisticated manufacturing processes forfabricating semiconductor devices in accordance with volume productiontechniques. For example, titanium and aluminum, as well as any alloysthereof, may be used as gate electrode materials which, however, mayspecifically be adapted in material composition and the like to obtainthe required work function and thus threshold adjustment. For example,in particular for sophisticated N-channel transistors, a moderately highwork function of approximately 4.1 electron volts may be difficult toachieve since typically the work function has to be adjusted on thebasis of an appropriate conductive barrier material that may have to beprovided to guarantee integrity of the high-k dielectric materialaccording to conventional process strategies. That is, according to aplurality of conventional process strategies, the high-k dielectricmaterial may be provided in an early manufacturing stage and may thuspass through a plurality of process steps, such as a plurality of etchsteps, high temperature treatments and the like, to complete the basictransistor configuration. Thereafter, in some of these approaches, acorresponding placeholder material, such as polysilicon, may be replacedby the desired metal electrode material, wherein, however, as previouslyexplained, an appropriate material composition may have to be providedto obtain in combination with a conductive barrier layer, which may haveto be maintained throughout the preceding process steps, the desiredwork function. For example, titanium nitride may frequently be used as aconductive barrier material which, however, may not readily allow a highwork function as may be required for sophisticated N-channeltransistors. On the other hand, avoiding the conductive barrier layerduring the preceding process steps may be less than desirable due to asignificant material erosion of the sensitive high-k dielectricmaterial. Similarly, a removal of the conductive cap layer prior to thedeposition of the work function metal may not represent a very promisingapproach due to a corresponding significant erosion of the high-kdielectric material.

In other conventional approaches, the high-k dielectric material and anappropriate work function metal for N-channel transistors may beprovided in an early manufacturing stage and may then be patterned toobtain high-k gate electrode structures. In this case, however, a verycomplex manufacturing sequence may be required for maintaining thedesired characteristics of the work function metal since frequently asignificant drift may be observed after any high temperature processes.Additionally, the band gap of the channel material of P-channeltransistors may be specifically adapted to the work function metal,which may frequently be accomplished on the basis of a silicon/germaniummaterial, which may locally be provided within the channel region of theP-channel transistors. Consequently, a very complex process sequenceprior to patterning the high-k metal gate electrodes may have to beperformed which, in combination with a high probability of shifting thecharacteristics of the work function metal, may result in reducedperformance of sophisticated semiconductor devices, which may renderthis approach, i.e., providing the high-k metal gate structure in anearly manufacturing stage, a less attractive approach.

The present disclosure is directed to various methods and devices thatmay avoid, or at least reduce, the effects of one or more of theproblems identified above.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an exhaustive overview of the invention. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

Generally, the present disclosure provides semiconductor devices andmethods in which work function and thus the transistor threshold voltagemay be adjusted on the basis of an appropriate metal species, which maybe selectively provided for N-channel transistors in a very advancedmanufacturing stage without unduly affecting the work function of thegate electrodes of P-channel transistors. In some illustrative aspectsdisclosed herein, the work function adjusting species for the N-channeltransistors may be comprised of a lanthanum which may enable, incombination with an appropriate metal-containing electrode materialacting as a conductive barrier material, such as titanium nitride,aluminum oxide and the like, a desired high work function for N-channeltransistors. In other illustrative aspects disclosed herein, a highlyefficient manufacturing sequence may be provided in which the selectiveadjustment of the work function may be accomplished without undulycontributing to overall process complexity, for instance in terms ofadditional lithography steps and the like, thereby providing superiorproduction yield due to the reduced process complexity, while at thesame time threshold adjustment of N-channel transistors, such as shortchannel transistors and long channel transistors within the samesemiconductor device, may be accomplished in a highly efficient manneron the basis of an appropriate work function adjusting species, such aslanthanum.

One illustrative method disclosed herein comprises forming a gateelectrode structure of a transistor above a semiconductor layer, whereinthe gate electrode structure comprises a placeholder electrode materialformed above a high-k gate insulation layer. The method furthercomprises forming drain and source regions of the transistor andremoving the placeholder electrode material. Furthermore, alanthanum-containing material layer is formed above the high-k gateinsulation layer. Finally, the method comprises forming ametal-containing electrode material on the lanthanum-containing materiallayer.

A further illustrative method disclosed herein comprises removing aplaceholder material of a first gate electrode structure of a firsttransistor and of a second gate electrode structure of a secondtransistor so as to expose a metal-containing material formed on ahigh-k gate insulation layer of the first and second gate electrodestructures, wherein the first and second transistors have differentconductivity types. The method further comprises forming a work functionadjusting material on the metal-containing material selectively in thefirst gate electrode structure. Furthermore, a first metal layer isformed on the work function adjusting material and a second metal layeris formed on the metal-containing material of the second gate electrodestructure wherein the second metal layer defines a work function of thesecond gate electrode structure in combination with the metal-containingmaterial.

One illustrative semiconductor device disclosed herein comprises a firstgate electrode structure of a first transistor. The first gate electrodestructure comprises a high-k gate insulation material, ametal-containing material formed on the high-k gate insulation material,a work function adjusting material formed on the metal-containingmaterial and a metal-containing electrode material. Additionally, thesemiconductor device comprises a second gate electrode structure of asecond transistor wherein the second gate electrode structure comprisesthe high-k gate insulation material, the metal-containing materialformed on the high-k gate insulation material, a first metal material, aconductive barrier material formed on the first metal material, the workfunction adjusting material positioned above the conductive barriermaterial and a second metal material.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIGS. 1 a-1 f schematically illustrate cross-sectional views of anN-channel transistor during various manufacturing stages in replacing aplaceholder electrode material of a gate electrode structure in a veryadvanced manufacturing stage and adjusting the work function on thebasis of a lanthanum species, according to illustrative embodiments; and

FIGS. 2 a-2 i schematically illustrate cross-sectional views of asemiconductor device during various manufacturing stages for formingtransistors of different conductivity type on the basis of asophisticated gate electrode structure, in which the work function andthus a threshold adjustment may be performed after completing the basictransistor configuration, according to illustrative embodiments.

While the subject matter disclosed herein is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Various illustrative embodiments of the invention are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The present subject matter will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present disclosure with details that arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present disclosure. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary and customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definition willbe expressly set forth in the specification in a definitional mannerthat directly and unequivocally provides the special definition for theterm or phrase.

Generally, the subject matter disclosed herein provides enhancedtechniques and devices wherein sophisticated high-k gate stacks may beformed after completing the basic transistor structure, thereby reducingthe probability of high threshold characteristics of sophisticatedtransistors compared to conventional strategies in which work functionadjusting metals may be provided in an early manufacturing stage.Furthermore, in some illustrative embodiments, a lanthanum species maybe incorporated into work function metal selectively in N-channeltransistors, thereby providing the possibility of obtaining a desiredhigh work function in combination with corresponding metal-containingmaterials, such as titanium nitride, aluminum oxide and the like, whichmay be provided to maintain integrity of the sensitive high-k gatedielectric material throughout the preceding manufacturing processes. Aswill be described later on in more detail, in some illustrativeembodiments, the lanthanum species may be provided on the basis of ahighly efficient manufacturing strategy without requiring additionallithography steps compared to conventional process techniques, in whichthe work function may be adjusted in a late manufacturing stage forP-channel transistors and N-channel transistors. For this purpose, insome illustrative embodiments, the lanthanum species may be providedafter forming a work function metal selectively for the P-channeltransistor and maintaining the work function adjusting characteristicsthereof on the basis of an appropriate conductive barrier material, suchas titanium nitride, thereby also providing an efficient diffusionbarrier for the lanthanum material to be deposited in a subsequentmanufacturing stage. As a consequence, a very efficient overallmanufacturing process may be provided for enabling the adjustment of thework function for different configurations of N-channel transistorssince sophisticated patterning regimes for appropriately providingspecific titanium/aluminum alloys for the different N-channel transistorconfigurations may be avoided.

FIG. 1 a schematically illustrates a field effect transistor 100 in avery advanced manufacturing stage. That is, the transistor 100 maycomprise a substrate 101, which may represent any appropriate carriermaterial, such as a silicon-based material, an insulating carriermaterial and the like, above which may be formed an appropriatesemiconductor layer 102, such as a silicon-based layer or any otherappropriate material including any species for adjusting the desiredoverall electronic characteristics of the material 102. It should beappreciated that the substrate 101 in combination with the semiconductorlayer 102 may form, at least locally within the substrate 101, asilicon-on-insulator (SOI) configuration when a corresponding buriedinsulating layer (not shown) is provided so as to “vertically” separatethe semiconductor layer 102 from the substrate 101. In a portion oractive region of the semiconductor layer 102, indicated as 102B, anappropriate dopant profile may be established so as to obtain drain andsource regions 103 of the transistor 100 wherein, as previouslydiscussed, the corresponding dopant profile may have any appropriateconfiguration so as to adjust the overall transistor characteristics,such as drive current, threshold voltage and the like. It should beappreciated, however, that at least the threshold voltage adjustment maybe completed in a later manufacturing stage, as will be described lateron. Furthermore, if required, metal silicide regions 104 may be formedin the drain and source regions in order to reduce the overall seriesresistance of a conductive path formed by the drain and source regions103 and a channel region 105 laterally positioned between the drain andsource regions 103.

The transistor further comprises a gate electrode structure 110, whichmay comprise a high-k gate insulation layer 111, which may thus compriseat least one material composition having a dielectric constant ofapproximately 10.0 or higher. It should be appreciated that the term“high-k gate insulation layer or gate dielectric material” may alsoinclude any material composition in which also conventional dielectricmaterials, such as silicon dioxide, silicon nitride and the like havinga relative permittivity of less than 10.0, may be present. For instance,in some embodiments, an oxide layer such as a native oxide and the likemay be formed on the channel region followed by a high-k dielectricmaterial, for instance one of the materials as previously referred to.Moreover, the high-k gate insulation layer 111 may be covered by ametal-containing material 112 which may also act as a barrier materialfor maintaining integrity of the high-k gate insulation layer 111 duringmanufacturing processes for forming the transistor 100, as illustratedin FIG. 1 a. In addition, the metal-containing material 112 may providesuperior conductivity compared to, for instance, doped polysiliconmaterial, which may represent a well-established gate electrodematerial. Thus, due to the moderately high conductivity of the material112, a corresponding generation of a depletion zone, as may typicallyoccur in polysilicon gate electrodes, may be avoided so that, incombination with the enhanced conductivity, superior performance of thetransistor 100 may be accomplished. As previously explained, themetal-containing material may have to provide an appropriate workfunction to adjust the finally desired threshold voltage of thetransistor 100, which may be accomplished by incorporating appropriatespecies in a later manufacturing stage. For example, themetal-containing material may be provided in the form of a titaniumnitride material, aluminum oxide and the like. Additionally, the gateelectrode structure 110 may comprise a dummy or placeholder electrodematerial 113, such as a silicon material and the like, which may,therefore, provide a high degree of compatibility with well-establishedmanufacturing techniques.

Furthermore, the gate electrode structure 110 may comprise a spacerstructure 114, which may have any appropriate configuration to providegate integrity during the preceding manufacturing processes and alsoprovide appropriate conditions during any implantation processes fordefining the drain and source regions 103 on the basis of animplantation. It should be appreciated that the configuration of thespacer structure 114 may thus change during the entire process sequencefor forming the transistor 100, depending on the specific requirementsof each of the various manufacturing stages. For example, the sidewallspacer structure 114 may comprise an appropriate liner material, such asa silicon nitride material, which may be formed on sidewalls of theplaceholder material 113 and in particular on sidewalls of the high-kgate insulation layer 111 to maintain overall integrity of thismaterial. Furthermore, the placeholder material 113 may also comprise ametal silicide 113A, depending on the process strategy used.

Furthermore, a dielectric layer 120 may be formed above the drain andsource regions 103 and the gate electrode structure 110, which may beprovided in the form of any appropriate material. For example, insophisticated applications, the dielectric material 120 may comprise ahigh internal stress level which may be transferred into the channelregion 105, thereby generating a specific type of strain therein, whichin turn may enhance the overall charge carrier mobility and thusconductivity of the channel region 105. For example, the dielectriclayer 120 may be provided in the form of a silicon nitride materialwhich may have a tensile stress component, and which may be advantageousfor enhancing performance of N-channel transistors for a standardcrystallographic configuration of the active region 102B. In thisrespect, it should be understood that a standard crystallographicconfiguration is to be understood as a silicon-based semiconductormaterial having a (100) surface orientation while the transistor lengthdirection, i.e., in FIG. 1 a the horizontal direction, is aligned to a<110> crystallographic axis. It should be appreciated, however, that anyother appropriate crystallographic orientation may be used, ifconsidered appropriate for the transistor 100. Furthermore, a furtherdielectric material 121, such as a silicon dioxide material, may beformed above the dielectric layer 120 wherein also in this case anyother appropriate material may be used, depending on the overall processand device requirements. Typically, the material 121 may represent aportion of an interlayer dielectric material that may be provided tomaintain integrity of the transistor 100 and provide a “platform” forthe formation of further metallization levels as may be required forconnecting a plurality of circuit elements, such as the transistor 100.

The transistor 100 as illustrated inure FIG. 1 a may be formed on thebasis of well-established process techniques for forming advancedtransistor elements. For example, after defining the active region 102B,for instance on the basis of providing appropriate isolation structures(not shown) and establishing a desired basic dopant profile, the gateelectrode structure 110 may be formed, for instance by providing anappropriate dielectric base layer, such as a silicon dioxide material,if desired, followed by the deposition of the high-k gate insulationlayer 111, which may be accomplished on the basis of chemical vapordeposition (CVD) techniques and the like. Thereafter, themetal-containing material 112 may be formed, for instance, by sputterdeposition, CVD and the like. Next, the placeholder material 113 may bedeposited, for instance, on the basis of low pressure CVD, therebyforming material such as silicon material in an amorphous state.Thereafter, highly sophisticated patterning techniques includingappropriate lithography processes may be performed to pattern thepreviously formed layer stack to obtain the gate electrode structure110, which may have an appropriate gate length, i.e., in FIG. 1 a thehorizontal extension of the metal-containing material 112. For example,the length of the gate electrode structure 110 may be selected to beapproximately 50 nm and less in sophisticated semiconductor devices.Thereafter, a portion of the spacer structure 114, for instance in theform of a nitride liner, may be provided to ensure integrity of thematerial 111 during the further processing. Next, the drain and sourceregions 103 may be formed in combination with appropriately selectedconfigurations of the spacer structure 114 so as to obtain a desiredcomplex dopant profile, as previously described. Thereafter,corresponding anneal processes may be performed in order to activate thedopants and re-crystallize implantation-induced damage. It should beappreciated that a plurality of additional process steps may berequired, for instance complex masking steps for forming the drain andsource regions 103 for different types of transistors, a plurality ofcleaning steps and the like, during which integrity of the material 111may be maintained by the metal-containing material 112 and the spacerstructure 114. Subsequently, the metal silicide regions 104, possibly incombination with the region 113A, may be formed by well-establishedsilicidation techniques, followed by a deposition of the material 120,which may be accomplished by plasma enhanced CVD techniques. Next, thedielectric material 121 may be deposited, for instance on the basis ofplasma enhanced CVD, thermally activated CVD and the like. Thereafter,as illustrated in FIG. 1 a, a material removal process 123 may beperformed to remove any excess material of the layer 121, therebyexposing at least an upper portion of the layer 120. The removal process123 may comprise selective etch recipes, chemical mechanical polishing(CMP) and the like.

FIG. 1 b schematically illustrates the transistor 100 after the removalprocess 123 of FIG. 1 a, thereby exposing an upper portion of thedielectric layer 120.

FIG. 1 c schematically illustrates the transistor 100 when exposed to afurther material removal process 124, which may represent, for instance,a selective etch process for selectively etching material of the layer120 with respect to the dielectric material 121. For this purpose, aplurality of well-established etch chemistries are available. In othercases, the process 124 may also include a mechanical removal component,for instance on the basis of CMP and the like. Thus, the gate electrodestructure 110 may be exposed during the removal process 124. Thereafter,a further material removal process may be performed to selectivelyremove the placeholder material 113, which may be accomplished on thebasis of chlorine-based etch chemistry, while, in other cases, highlyselective wet chemical etch recipes may be used. For example, an etchchemistry on the basis of tetra methyl ammonium hydroxide (TMAH) may beused in an appropriate concentration and temperature so that amoderately high etch rate may be obtained for silicon material, while ahigh degree of selectivity with respect to silicon nitride, silicondioxide and the like may be provided by this etch chemistry. Moreover,during the corresponding etch process, the metal-containing material 112may act as an efficient etch stop layer, thereby ensuring integrity ofthe high-k gate insulation layer 111.

FIG. 1 d schematically illustrates the transistor 100 in a furtheradvanced manufacturing stage in which a work function adjusting materiallayer 116 may be formed on sidewalls of an opening 115 formed in thegate electrode structure 110 after the removal of the placeholdermaterial, as described above. In one illustrative embodiment, the layer116 may comprise a lanthanum species that may, in combination withmetal-containing material 112, provide a desired high work function, forinstance of approximately 4.0 electron volts and higher, so as to enablean appropriate adjustment of the threshold voltage of the transistor100. For this purpose, any appropriate deposition process 126 may beperformed, for instance, a sputter deposition process, a CVD process, anatomic layer deposition (ALD) process and the like. For example, thelayer 116 may be provided with a thickness of approximately 1-25 Å, asrequired for appropriately adjusting the finally desired work function,which may be accomplished during a heat treatment during a latermanufacturing stage.

FIG. 1 e schematically illustrates the transistor 100 in a manufacturingstage in which an appropriate metal material 117 may be deposited on thebasis of any appropriate deposition process 127 so as to fill theopening 115 (FIG. 1 d). For example, any appropriate metal-containingmaterial may be used for the layer 117, depending on the overall processrequirements. Similarly, any appropriate deposition technique may beused during the process 127, such as CVD, sputter deposition,electroless plating and the like. Thereafter, any excess material of thelayer 117 may be removed, for instance, by electrochemical etching,electro CMP, CMP and the like, wherein residues of the work functionadjusting material 116 may also be removed from horizontal portions ofthe transistor 100.

FIG. 1 f schematically illustrates the transistor 100 in a furtheradvanced manufacturing stage in which the transistor 100 may besubjected to a heat treatment 128 in order to initiate the incorporationof a work function adjusting species of the layer 116 into themetal-containing material 112 so as to obtain the desired work function.For example, the heat treatment 128 may be performed at elevatedtemperatures of approximately 400-600° C., thereby “reflowing” the layer116 so as to achieve a certain degree of diffusion into the layer 112.For example, the lanthanum species may be incorporated with a certaindegree, depending on the initial thickness of the layer 116 and theprocess parameters of the treatment 128. Thus, in this manner, a desiredhigh work function for the transistor 100 and thus the correspondingthreshold voltage may be adjusted, for instance on the basis oflanthanum, thereby enabling the formation of sophisticated N-channeltransistors, such as short channel transistors and the like.

With reference to FIGS. 2 a-21, further illustrative embodiments willnow be described in which efficient overall manufacturing sequence maybe accomplished by providing an appropriate work function adjustingspecies for N-channel transistors, such as a lanthanum species, withoutunduly affecting the work function adjustment of P-channel transistors.

FIG. 2 a schematically illustrates a cross-sectional view of asemiconductor device 250 comprising a first transistor 200 and a secondtransistor 200A in a very advanced manufacturing stage. In oneillustrative embodiment, the first transistor 200 may represent anN-channel transistor while the transistor 200A may represent a P-channeltransistor. Furthermore, the transistors may have basically aconfiguration as previously described with reference to the transistor100, wherein it should be appreciated that the transistors 200, 200A maydiffer from each other in their conductivity type and thus in thecorresponding dopant profiles and dopant material. For convenience, anysuch differences are not shown in FIG. 2 a. Thus, the transistors 200,200A may comprise respective gate electrode structures 210, 210A,respectively, which may thus include a high-k gate insulation layer 211,211A, a metal-containing material 212, 212A, which may also act as aconductive barrier or cap layer for the layers 211, 211A. Furthermore, asidewall spacer structure 214, 214A may be provided. It should beappreciated that, in some illustrative embodiments, the components ofthe gate electrode structures 210, 210A may be identical due to a commonmanufacturing sequence, while, in other cases, if required, at leastsome of these components may be different in the transistors 200, 200A.Furthermore, in the manufacturing stage shown, respective openings 215,215A are provided within the corresponding gate electrode structures210, 210A, respectively.

Similarly, the transistors 200, 200A may comprise respective activeregions 202B, 202A formed in a semiconductor layer 202, which may beprovided above a substrate 201. Furthermore, corresponding drain andsource regions 203, 203A, possibly in combination with metal silicideregions 204, 204A, may be provided in the active regions 202B, 202A.With respect to any of these components, the same criteria may apply aspreviously explained with reference to the transistor 100.

Furthermore, the semiconductor device 250 may be formed on the basis ofsimilar process techniques as discussed above. It should be appreciated,however, that, due to the different conductivity type, a correspondingmasking regime may be used for introducing appropriate doping speciesinto the active regions 202B, 202A. Thus, after completing the basictransistor configuration of the device 250, one or more dielectriclayers 220, 220A may be formed, for instance in the form of stresseddielectric materials, to establish a desired type of strain in thetransistors 200, 200A. For example, a tensile stress component may beprovided for the transistor 200, while a compressive stress componentmay be used in the layer 220A. For this purpose, well-establishedprocess techniques may be applied to selectively form the layer 220above the transistor 200 and the layer 220A above the transistor 200A.It should be appreciated, however, that any other appropriate processregime may be applied if different stress components may not berequired. Thereafter, the dielectric material 221 may be deposited andmay be reduced in thickness so as to expose upper portions of the gateelectrode structures 210, 210A, as previously explained. Next, an etchprocess 227, for instance on the basis of etch chemistries as discussedabove, may be performed to obtain corresponding openings 215, 215A inthe gate electrode structures 210, 210A, thereby exposing themetal-containing materials 212, 212A.

FIG. 2 b schematically illustrates the semiconductor device 250 during adeposition sequence 228, in which a metal material 217A may bedeposited, which may appropriately be selected so as to define a workfunction for the transistor 200A in combination with the remainingportion of the material 212A. For this purpose, any appropriatemetal-containing material may be used, such as aluminum, titanium andthe like. For this purpose, any appropriate deposition technique may beapplied, for instance sputter deposition, in which a high degree ofdirectionality may be achieved, thereby reliably forming material on themetal-containing material 212A within the opening 215A. It should beappreciated that the material 217A may be deposited within the opening215. Thereafter, the deposition sequence 228 may comprise a furtherdeposition step in which a conductive barrier material 218, such astitanium nitride and the like, may be deposited with an appropriatethickness, such as one to several nanometers, in order to providesufficient diffusion hindering capabilities during the subsequentprocessing. For this purpose, any appropriate deposition technique maybe used.

FIG. 2 c schematically illustrates the semiconductor device 250 in amanufacturing stage in which the transistor 200A may be masked by anetch mask 229, such as a resist mask, while the transistor 200 isexposed to an etch ambient 230 that may be established on the basis ofan etch chemistry for removing the materials of a layer 218 and 217Aselectively with respect to the dielectric materials 221, 220 and thespacer structure 214. For example, a plurality of wet chemical andplasma assisted etch recipes are available for removing metal materialselectively to dielectric materials, such as silicon nitride, silicondioxide and the like. During the process 230, the conductive barriermaterial 218 may be removed first and subsequently an appropriate etchchemistry may be used for removing the material 217A from the transistor200, wherein, at a final stage of the etch process 230, the material 212may act as an etch stop or etch control material, thereby maintainingintegrity of the underlying high-k gate insulation layer 211.

FIG. 2 d schematically illustrates the semiconductor device 250 afterremoval of the etch mask 229 (FIG. 2 c). The device 250 may beappropriately prepared for receiving a work function adjusting speciesfor the transistor 200, wherein the conductive barrier material 218 mayrepresent an appropriate barrier in the transistor 200A, therebyavoiding undue interaction of the work function adjusting species withthe underlying material 217A, which may thus maintain its work function,thereby also maintaining the required threshold voltage for thetransistor 200A.

FIG. 2 e schematically illustrates the semiconductor device 250 whenexposed to a deposition process 226, during which a work functionadjusting species, such as a lanthanum-comprising material layer 216,may be deposited above the transistors 200, 200A. Consequently, duringthe process 226, the material 216 may be formed on the metal-containingmaterial 212, while, in the transistor 200A, the material 216 may beformed on the conductive barrier material 218, thereby separating thework function metal 217A from the work function adjusting layer 216.With respect to the deposition process 226, the same criteria may applyas previously explained with reference to the deposition process 126 asillustrated in FIG. 1 d. Furthermore, as discussed above, a thickness ofthe layer 216 may be selected in a range of approximately 1-25 Å.

FIG. 2 f schematically illustrates the semiconductor device 250 during afurther metal deposition process 227, during which an appropriate metal217 may be formed so as to fill the openings 215, 215A. For thispurpose, any appropriate material may be used since the work functionfor the transistor 200 may be adjusted on the basis of the layer 216 incombination with the metal-containing material 212, while, in thetransistor 200A, the work function may be determined by the material212A in combination with the metal 217A, which may be reliably separatedfrom the materials 216 and 217 by the conductive barrier material 218.The deposition process 227 may be performed on the basis of anyappropriate deposition technique, as is also discussed above withreference to the deposition process 127 as illustrated in FIG. 1 e.

FIG. 2 g schematically illustrates the semiconductor device 250 in afurther advanced manufacturing stage. In this embodiment, a heattreatment 228 may be performed to initiate the incorporation of aspecies of the layer 216 in the material 212, as is also previouslyexplained with reference to the transistor 100 when referring to theheat treatment 128, as illustrated in FIG. 1 f. It should be appreciatedthat the heat treatment 228 may be performed prior to the removal of anyexcess material of the layer 217, as illustrated in FIG. 2 g, while, inother cases, the corresponding heat treatment may be performed afterremoving any excess material, as is for instance explained withreference to the transistor 100. Similarly, for the transistor 100, acorresponding heat treatment 218 (FIG. 1 f) may be performed prior toremoving any excess material. Consequently, based on the characteristicsof the layer 216, such as the material composition, the thicknessthereof and the like, in combination with the process parameters of theprocess 228, the degree of interaction between the materials 216 and 212may be adjusted, thereby also adjusting the work function and thus thethreshold voltage of the transistor 200. As previously explained, thelayer 216 may be provided in the form of a lanthanum layer or may haveincorporated therein a moderately high concentration of lanthanum,thereby obtaining the desired high work function as may be required forsophisticated N-channel transistors, as discussed above.

FIG. 2 h schematically illustrates the semiconductor device 250 during amaterial removal process 231, during which excess material of the layers217, 216, 217A and 218 (FIG. 2 g) may be removed. For this purpose, anyappropriate process technique, either individually or in combination,may be applied, such as CMP, electro CMP, etching, electro etching andthe like.

FIG. 2 i schematically illustrates the semiconductor device 250 afterproviding a further interlayer dielectric material 222, for instance inthe form of silicon dioxide and the like, which may be provided by anyappropriate deposition process, such as plasma enhanced CVD, thermallyactivated CVD and the like. Thereafter, the further processing may becontinued by forming appropriate contact openings in the materials 222,221, 220 and 220A in order to form a contact to respective contact areasof the transistors 200, 200A. The corresponding process sequence may beperformed on the basis of any well-established process techniques.

As a result, the present disclosure provides semiconductor devices andmanufacturing techniques in which the work function and thus thethreshold voltage of sophisticated transistors, such as N-channeltransistors of different configuration, may be adjusted in a latemanufacturing stage on the basis of a highly efficient overallmanufacturing sequence. For this purpose, in some illustrativeembodiments, a lanthanum species may be incorporated so as to initiate amaterial inter diffusion for adjusting the work function of one type oftransistor while substantially suppressing an inter diffusion of thelanthanum species in the other type of transistor, which may beaccomplished by selectively providing an appropriate conductive barriermaterial. Using the lanthanum species as a work function adjustingspecies may therefore enable obtaining moderately high work functions,as may be required for N-channel transistors, thereby contributing toenhanced transistor performance and increased production yield, sincethe efficient overall manufacturing flow may significantly reduce anyprocess-related defects, which may typically be associated with highlycomplex process regimes for adjusting the work function of N-channeltransistors of different configuration, such as short channeltransistors and long channel transistors.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. For example, the process steps set forth above may beperformed in a different order. Furthermore, no limitations are intendedto the details of construction or design herein shown, other than asdescribed in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of theinvention. Accordingly, the protection sought herein is as set forth inthe claims below.

1. A method, comprising: forming a gate electrode structure of atransistor above a semiconductor layer, said gate electrode structurecomprising a placeholder electrode material formed above a high-k gateinsulation layer; forming drain and source regions of said transistor;removing said placeholder electrode material; forming alanthanum-containing material layer above said high-k gate insulationlayer; and forming a metal-containing electrode material on saidlanthanum-containing material layer.
 2. The method of claim 1, whereinforming said gate electrode structure comprises forming ametal-containing barrier material on said high-k gate insulation layerand forming said placeholder electrode material on said metal-containingbarrier material.
 3. The method of claim 2, wherein saidlanthanum-containing material layer is formed on said metal-containingbarrier material.
 4. The method of claim 3, further comprisingperforming a heat treatment so as to initiate diffusion of lanthanumspecies into said metal-containing barrier material.
 5. The method ofclaim 1, wherein said transistor represents an N-channel transistor. 6.The method of claim 1, further comprising forming a second gateelectrode structure of a second transistor that has a differentconductivity type as said transistor, wherein said second gate electrodestructure comprises a second high-k gate insulation layer and a secondplaceholder electrode material formed above said second high-k gateinsulation layer and wherein said placeholder electrode material andsaid second placeholder electrode material are removed by performing acommon removal process.
 7. The method of claim 6, further comprisingforming a metal layer above said first and second gate electrodestructures so as to adjust a work function of said second gate electrodestructure prior to forming said lanthanum-containing material layer. 8.The method of claim 7, further comprising forming a conductive barrierlayer on said metal layer prior to forming said lanthanum-containingmaterial layer.
 9. The method of claim 8, further comprising removingsaid conductive barrier layer and said metal layer selectively fromabove said high-k gate insulation layer of said gate electrode structureprior to forming said lanthanum-containing material layer.
 10. Themethod of claim 9, further comprising forming a metal-containingmaterial above said gate electrode structure and said second gateelectrode structure after forming said lanthanum-containing materiallayer.
 11. The method of claim 1, wherein said lanthanum-containingmaterial layer is formed with a thickness of approximately 1-25 Å.
 12. Amethod, comprising: removing a placeholder material of a first gateelectrode structure of a first transistor and a second gate electrodestructure of a second transistor so as to expose a metal-containingmaterial formed on a high-k gate insulation layer of said first andsecond gate electrode structures, said first and second transistorshaving different conductivity types; forming a work function adjustingmaterial on said metal-containing material selectively in said firstgate electrode structure; forming a first metal layer on said workfunction adjusting material; and forming a second metal layer on saidmetal-containing material of said second gate electrode structure, saidsecond metal layer defining a work function of said second gateelectrode in combination with said metal-containing material.
 13. Themethod of claim 12, wherein forming said work function adjustingmaterial comprises forming a lanthanum-containing material.
 14. Themethod of claim 12, wherein forming said second metal layer comprisesforming said second metal layer on said metal-containing material ofsaid first and second gate electrode structures and removing said secondmetal layer selectively from said first gate electrode structure. 15.The method of claim 14, further comprising forming a conductive barrierlayer on said second metal layer of said second gate electrode structureprior to forming said work function adjusting material.
 16. The methodof claim 15, wherein forming said work function adjusting material onsaid metal-containing material selectively in said first gate electrodestructure comprises forming said work function adjusting material onsaid metal-containing material and said conductive barrier material. 17.The method of claim 12, further comprising performing a heat treatmentso as to initiate incorporation of a metal species of said work functionadjusting material into said metal-containing material selectively insaid first gate electrode structure.
 18. The method of claim 16, whereinsaid first metal layer is formed on said work function adjustingmaterial formed on said conductive barrier material of said second gateelectrode structure.
 19. The method of claim 12, wherein saidplaceholder material of said first and second gate electrode structuresis removed after forming drain and source regions of said first andsecond transistors.
 20. The method of claim 12, wherein said firsttransistor represents an N-channel transistor.
 21. A semiconductordevice, comprising: a first gate electrode structure of a firsttransistor, said first gate electrode structure comprising a high-k gateinsulation material, a metal-containing material formed on said high-kgate insulation material, a work function adjusting material formed onsaid metal-containing material and a metal-containing electrodematerial; and a second gate electrode structure of a second transistor,said second gate electrode structure comprising said high-k gateinsulation material, said metal-containing material formed on saidhigh-k gate insulation material, a first metal material, a conductivebarrier material formed on said first metal material, said work functionadjusting material formed above said conductive barrier material and asecond metal material.
 22. The semiconductor device of claim 21, whereinsaid work function adjusting material comprises lanthanum.
 23. Thesemiconductor device of claim 21, wherein said work function adjustingmaterial has a thickness of approximately 1-25 Å.
 24. The semiconductordevice of claim 21, wherein said metal-containing electrode material ofsaid first gate electrode structure and said first and second metalmaterials of said second gate electrode structures comprise at least oneof titanium and aluminum.
 25. The semiconductor device of claim 21,wherein said first transistor is an N-channel transistor.